The Provider Backbone Bridge Traffic Engineering (PBB-TE) is an Ethernet based solution for provider network. In comparison with a traditional Ethernet, this solution removes the mechanisms of self-learning, spanning tree and flooding, and establishes Ethernet forwarding paths by network management systems (NMS) or control protocols which can operate on Ethernet forwarding table. Unlike the traditional connectionless Ethernet, the PBB-TE is a connection-oriented technology, i.e. in PBB-TE a connection is established prior to the service transmission. PBB-IE is a formal denomination in the Standards organization for the technique which is previously called “Provider Backbone Transport (PBT)”. In this application document, the wording “PBB-TE” will be used hereinafter.
In PBB-TE, a Medium Access Control (MAC) destination address and a Virtual Local Area Network (VLAN) Identifier (ID) are used together to identify a unidirectional forwarding path. A PBB-TE packet is forwarded according to the destination MAC address and the VLAN ID which are encapsulated in the packet header. If PBB-TE switch receives a PBB-TE packet with DA/VID pair which not present in the forwarding table, the PBB-TE packet will be discarded instead of being broadcast. The forwarding entries are installed by management plane or the control plane, not by utilization of spanning tree protocol and an address learning mechanism.
A provider network always requires maintenance mechanisms to provide the capability of monitoring, diagnostic and protection, etc. The maintenance mechanism is referred to as Operation, Administration and Maintenance (OAM) mechanism in ITU-T, and as Connectivity Fault Management (CFM) mechanism in IEEE. Because the PBB-TE standard is developed in IEEE at present, this application document will use the IEEE denomination, i.e. CFM, hereinafter. Though the mechanism may also be applied to adaptation to the OAM mechanism of ITU-T.
The traditional Ethernet is a kind of connectionless technology. So, the CFM mechanism of the traditional Ethernet is also connectionless, which includes:
1. Continuity Check (CC) mechanism. The procedure for the CC mechanism is as follows. The Maintenance association End Points (MEPs) periodically send CC messages (CCM) to other MEPs in the same Maintenance Association (MA). If no CC messages have been received from any MEP within 3.5 times of the CC interval, alerts will be generated to notify that there may be some failure on the connection. Information, such as an MEP list and MD level, are preconfigured on the MEP. Faults, such as link failure, misconnection, can be detected by CC mechanism. There are two kinds of CC messages, multicast CC message and Unicast CC message. The multicast CCM is applicable to all types of connection monitoring. The destination address of multicast CC message is a special CFM multicast address. A multicast CC message is broadcast to all other MEPs in the same MA. Unicast CC is applicable to point-to-point connection monitoring. The destination address of unicast CC message is the address of the remote MEP. A unicast CC message is forwarded along a unicast forwarding path.
2. Loopback (LB) mechanism. LB is typically used for fault location A loopback initiator transmits an LB message (LBM) to a destination Maintenance Point (MP). When receiving a LBM, the destination maintenance point will return an LB reply (LBR) to the loopback initiator. If the loopback initiator has not received an expected LBR within a certain period of time, it means that a connectivity fault is present between the loopback initiator and the destination maintenance point. Multicast LB is applicable to loopback check between a MEP and all other MEPs in the same MA. The destination address of a multicast LB message is a special CFM multicast address. Unicast LB is applicable to point-to-point loopback check. The destination address of a unicast LB message is the address of an MIP/MEP. A unicast LB message is forwarded along a unicast path.
3. Linktrace (LT) mechanism. A linktrace message (LTM) is transmitted by a MEP linktrace initiator in order to perform path discovery and fault isolation. When receiving the LTM, a maintenance point (MP) will return a unicast linktrace reply (LTR) to the linktrace initiator, and issues a new LTM towards the target MEP. Thus, the linktrace initiator can learn all the nodes on the forwarding path. If no expected LTR is returned, a fault can be located by the LTRs previously returned. LTM messages are encapsulated with a special CFM multicast address. However, the LTM is forwarded along the unicast path because the outport is determined by the target MAC address carried in the LTM PDU.
However, the CFM mechanisms for connectionless Ethernet can not be used to monitor PBB-TE connection. A CFM message is forwarded according to destination address (DA) and VLAN ID. However, in PBB-TE, the DA/VID pair is used to identify a PBB-TE path, but not the destination address of a message, so the CFM functions which need process CFM messages by intermediates node of a PBB-TE path can not be implemented by previous art, especially for monitoring sub network connection (SNC). For the purpose of convenience, a complete connection will be referred to as a “path”, and a monitored part will be referred to as a “connection” hereinafter in this application document.
Further, for the CFM mechanisms which need reply messages, such as LB, and LT, the message may be returned directly in an Ethernet, because paths in the Ethernet are bidirectional. However in the PBB-TE, a bidirectional path has different identifiers, particularly different VLAN IDs. Moreover in the PBB-TE, a message unknown to a node will be discarded instead of being broadcast. In this way, with the CFM mechanisms of Ethernet, the reply message may not be transmitted and received correctly in a PBB-TE network.